It is essential for a living organism to interact with and adjust to the environment by generating responses at molecular, cellular, and system levels. In some cases, these changes result in life-long or even multi- generational changes to physiology and behavior. Understanding the interactions between our genes and the environment is vital to our understanding of addiction. Therefore, molecular and genetic tools to dissect and discover these interactions need to be developed. Of critical importance is the bridge between genetics and behavior that is gated by the stress response. A stress response is a physiological and/or behavioral response to a real or perceived threat or stressor that helps maintain or restore normal balance or homeostasis. When a stressor threatens homeostasis, a diverse suite of neuronal, endocrine, and autonomic response mechanisms can be utilized to regain the status quo. In addition to the immediate changes in response to a stressor, long-term changes in the neural network or epigenetic transcriptome can record the molecular memory of this event and thereby alter future responses to similar stressors. The clinical significance of stress-aggravated disorders is extremely high, and can occur when a stressor is too strong (acute), occurs too often (chronic), or is recorded to the epigenome incorrectly and/or during critical developmental periods. The stress response, particularly glucocorticoids, affects the onset, severity, withdrawal, and relapse of addiction. Smoking and thereby nicotine addiction, is the number one preventable cause of death in the world. This proposal will use a genetic model organism, zebrafish (Danio rerio), to study the interaction of the stress response and behavioral sensitization to a psychostimulant- nicotine. Specifically this application will characterize glucocorticoid receptor activation following exposure to nicotine; characterize changes in behavioral sensitization to nicotine caused by stressors, exogenous corticosteroids, or antagonists to the stress response; and perform a screen for modifiers of the stress response. The goal of this proposal is to build a foundation of data to accelerate the use of the genetically tractable, high-throughput zebrafish model to study the interaction of stress and addiction. Innovative elements of this grant use genetic sensor fish to permit spatio-temporal visualization of glucocorticoid receptor activation in all brain tissues in response to drug exposure or other stressors, and a unique mutant library resource of transposon-based insertional mutant zebrafish to do the first forward genetic screen for modifiers of the stress response in a vertebrate. !